Photon Conversion Efficiency Research Articles

Ruthenium (II) complexes bearing N‐heterocyclic carbene‐based C^N donor sets in dye‐sensitized solar cells

We present the syntheses of ruthenium (II) complexes bearing an N‐heterocyclic carbene (NHC)‐based C^N donor set and an NCS ligand and evaluate their use as photosensitizers in dye‐sensitized solar cells (DSSCs). These complexes deploy a monocarboxylic acid‐functionalized terpyridine (tpy)/phenyl‐tpy to anchor with the TiO2 of the photoanodes. Results show that the complexes devoid of the phenyl spacer between the acid anchor and the tpy harvest the visible light more effectively. Absorption of the visible light transfers the electron density from the ruthenium, NHC, and the NCS donors to the tpy acceptor (1MRuLdonorLacceptorCT). Stronger MRuLdonor σ‐bonds in the complexes with opposite NHC and tpy ligand configuration render facile ruthenium‐centered oxidation. In contrast, the metal‐centered oxidation of complexes with trans‐oriented NHC and NCS ligands is relatively difficult. However, these complexes display higher photon conversion efficiency (PCE) in DSSCs. One of them shows PCE of 3.44%, which is ~70% of the standard N3 dye, under similar conditions. A longer electron lifetime and the lowest charge transfer resistance at the TiO2/electrolyte interface derived from the electrochemical impedance spectra accounts for the enhanced PCE. Insights into the oxidized dye regeneration in a DSSC setup, obtained from the computed Hirshfeld charges and spin density, depict the essential role of iodide anion in dye regeneration. This report summarizes our investigation of photophysics, electronic structure calculations, and the electrochemical study of all newly prepared complexes and their use as photosensitizers in DSSCs.

Boosted photocatalytic activity of LaFeO3/Ag3PO4 heterojunction via carbon quantum dots: Higher conductivity, stability, and dispersivity

Several restrictions including low photon conversion efficiency, unabiding material stability, and aggregation behavior hinder large scale applicability of conventional semiconductor photocatalysts for pollutants removal. In this work, the inexpensive carbon quantum dots (CQDs) was synthesized by facile one-step hydrothermal process and introduced into LaFeO3/Ag3PO4 nanocomposites for photodegradation of organic dyes. The morphology, surface chemical states, optical and electrochemical properties of as-prepared samples were systematically investigated using HRTEM, FT-IR, XPS, UV–vis,UV–vis, and PL. LaFeO3/Ag3PO4 with 3 wt% of CQDs presented the higher photocatalytic activity with 97.3 % removal rate of methylene blue (MB) organic dyes under 60 min visible light irradiation, which were three times that of the binary LaFeO3/Ag3PO4 composites. The effect of initial pH and co-existing inorganic ions on MB removal efficiency, particle aggregation behavior during photocatalytic process, and dominant reaction active species were investigated. The results showed that CQDs significantly improved the photoelectrochemical (PEC) performance of LaFeO3/Ag3PO4 composites, as well as protected Ag3PO4 from photo corrosion due to variation of electronic transfer path in composite material. Benefitting from numerous oxygen and nitrogen-containing functional groups, CQDs as a dispersing agent, improved water dispersibility and wettability of photocatalyst particles, and inhibited agglomeration of nano-photocatalyst on photocatalytic reactivity. These findings highlight the potential utility of CQDs in assisting a rapidly photodegrading molecular dye in an aqueous solution.

Crystallographic, optical, photoluminescence and electrical properties of CuS quantum dots: Influence of ethylenediamine

Copper sulfide (CuS) is a semiconductor widely used for quantum dot sensitized solar cell applications due to its photocatalytic activity. The hydrothermal technique was used to synthesize the copper sulfide quantum dots. The distilled water and ethylenediamine are served as solvents with different combinational ratios. According to TEM studies, the particles' size increased as the solvents' ratio decreased. XRD patterns revealed that the synthesized CuS QDs are polycrystalline with a hexagonal structure. UV–vis results showed that the absorption of CuS QDs is from 310 nm to 320 nm, and the band gap of synthesized quantum dots is found to be ∼3.7 eV. Photoluminescence spectra illustrate that the CuS quantum dot emission spectrum was observed at 475 nm (blue emission) and 570 nm (green emission). The highest power conversion efficiency (0.5390 %) was received for the 25:75 ratio of DI Water/EN using the CuS quantum dot. It is observed as better photon conversion efficiency among all the ratios with lesser charge recombination.

Electron beam pumping improves the conversion efficiency of low-frequency photons radiated by perovskite quantum dots

This research argues that using an electron beam with high kinetic energy to pump perovskite quantum dots can significantly boost the efficiency of the low-frequency photon radiation conversion. Firstly, we measure the random lasing threshold and luminescence threshold of CsPbX 3 films pumped by an electron beam. Then, we simulate the spatial distribution of the electron beams in CsPbX 3 films. Combined with the above data, a low-frequency photon radiation conversion model based on the electron pumped perovskite quantum dots is presented. This could be a way to create a terahertz source with a high-power output or to multiply the terahertz power.

Combination of co-sensitization and Förster resonance energy transfer in natural-synthetic dye sensitized solar cells

A new approach for performance enhancement of dye sensitized solar cells (DSSC) is presented in this paper using a combination of co-sensitization method and Förster resonance energy transfer (FRET) from natural pigments to synthetic pigment. Although co-sensitization is the most common method for spectral extension of DSSCs, the loading of pigment on the semiconductor is restricted in this method. To overcome this problem, here, the TiO2 was sensitized directly by an organic synthetic pigment that has suitable anchor groups, while the natural pigments were used as energy-donors without the need for direct bonding to the TiO2. The natural pigments were selected in such a way that satisfies the FRET requirements. Three natural pigments were inexpensively extracted from plants to prepare a broad absorption spectrum. This issue was evaluated by UV–Visible analyses. It was found that the natural pigments can be more useful in the spectral expansion if applied in the FRET process as energy-donors due to their weaker anchoring groups compared to synthetic pigment. The anchoring groups of the extracted pigments were evaluated by FT-IR analysis. Also, the FRET occurrence between the natural pigments with the synthetic pigment was examined by photoluminescence spectroscopy. The results indicated a proper spectral overlap and emission quenching between these pigments. Finally, the opto-electrical performances of the DSSCs fabricated by the proposed method were investigated by J-V characteristics, electrochemical Impedance spectroscopy (EIS), and induced photon conversion efficiency (IPCE) compared with conventional co-sensitization methods (cocktail and sequential methods). The efficiencies obtained for these two conventional methods were 1.8% and 2.2%, respectively, while an efficiency of 2.9%. was provided by the proposed approach.

Solar light driven photoelectrochemical water splitting using Mn-doped CdS quantum dots sensitized hierarchical rosette-rod TiO2 photoanodes

Herein we investigated the photoelectrochemical performance of manganese (Mn) doped cadmium sulfide (CdS) quantum dots (QDs) decorated onto the surface of hierarchical double-layered rosette-rod titanium dioxide (TiO2) photoanode. The rosette-rod TiO2 architectures are synthesized by two steps hydrothermal process while Mn-doped CdS QDs deposition is taken out by successive ionic layer adsorption and reaction (SILAR) approach. Two different kinds of structures exist simultaneously in rosette-rod TiO2, one-dimensional TiO2 nanorod arrays present at the bottom, while the upper three-dimensional nano rosette consists of small TiO2 nanorods as building units. Photoelectrochemical performance of the as-prepared photoanodes are explored in terms of photocurrent density and applied biased to photon conversion efficiency by varying Mn concentration and the number of SILAR cycles to find the best performing photoanodes. Linear sweep voltammetry results show that 35 mM shows the maximum photo-current density of 2.12 mA cm−2 at 1.23 VRHE with a maximum photoconversion efficiency of ∼1.61% at 0.4 VRHE, while 8 numbers of SILAR cycles shows the highest photo current–density of 2.73 mA cm−2 at 1.23 VRHE and maximum photoconversion efficiency of 2.19% at 0.2 VRHE.

Hot carrier extraction from plasmonic-photonic superimposed heterostructures.

Plasmonic nanostructures have been exploited in photochemical and photocatalytic processes owing to their surface plasmon resonance characteristics. This unique property generates photoinduced potentials and currents capable of driving chemical reactions. However, these processes are hampered by low photon conversion and utilization efficiencies, which are issues that need to be addressed. In this study, we integrate plasmonic photochemistry and simple tunable heterostructure characteristics of a dielectric photonic crystal for the effective control of electromagnetic energy below the diffraction limit of light. The nanostructure comprises high-density Ag nanoparticles on nanocavity arrays of SrTiO3 and TiO2, where two oxides constitute a chemical heterojunction. Such a nanostructure is designed to form intense electric fields and a vectorial electron flow channel of Ag → SrTiO3 → TiO2. When the plasmonic absorption of Ag nanoparticles matched the photonic stopband, we observed an apparent quantum yield of 3.1 × 10-4 e- per absorbed photon. The contributions of light confinement and charge separation to the enhanced photocurrent were evaluated.

High-performance organic upconversion device with 12% photon to photon conversion efficiency at 980 nm and bio-imaging application in near-infrared region.

We demonstrated an organic upconversion device (UCD) successfully converted input NIR light (850-1310 nm) into 524 nm green emission. The UCD under 980 nm light irradiation exhibits a high photon to photon conversion efficiency of 12%. In addition, the linear dynamic range reaches 72.1 dB and the maximum on/off ratio of luminance reaches 4.4×104, which guarantee the clarity of imaging from 850 to 1310 nm. The UCD in this work has the characteristics of high efficiency and long wavelengths detection, and it makes some senses for long wavelengths NIR bio-imaging in further researches.

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Recent Advances in Luminescent Downconversion: New Materials, Techniques, and Applications in Solar Cells

AbstractNumerous investigations have been done in pursuing phosphors with quantum yield (QY) greater than unity in terms of downconversion (DC) strategies, as well as applications in display, lighting, and particularly in novel solar cells with efficiency exceeding the Shockley–Queisser limit (≈30%). It is of significant interest that: i) DC of one high‐energy photon to two or more low‐energy photons is widely found in lanthanide and/or transition‐metal ions activated materials; ii) broadening of absorption spanning ultraviolet/blue range is achieved by introducing sensitizers with spin‐allowed transitions and especially by combining the advancing perovskite quantum dots, nanostructures, and organic dye molecules; iii) internal QY ≫ 1 and even measured QY > 1 are claimed in many near‐infrared (NIR) DC systems; iv) applications of downconverting layer atop commercial solar cells are performed to increase the photon conversion efficiency. In this review, the development of DC in theories, concepts, and experiments is first summarized, then the breakthrough in visible‐DC is briefly highlighted, NIR‐DC with latest progresses in models, materials, techniques as well as the corresponding optimizations and practices as effective downconverting layers is elaborated, and finally concluding remarks and perspectives in advancing NIR‐DC and applications in novel solar cells are given.

The investigation of stimulated Raman scattering in gases under di-harmonic pumping

An investigation was made of the features of the competing effects in gaseous stimulated Raman scattering (SRS) under single and di-harmonic pumping. Firstly, the one aim of this work was to observe the variations of forward and backward SRS generation in CH4 gas under di-harmonic pumping composed of 1064 nm and 532 nm lasers. At low pressure di-harmonic pumping suppressed backward SRS of 1064 nm beam, and enhanced its output energy of forward SRS. Secondly, di-harmonic pumping of 1064 nm and 1.54μm radiations obviously suppressed stimulated rotational Raman scattering, and enhanced its stimulated Raman vibrational scattering at high pressure of H2 gas. A 13.6 mJ 4.30μm mid-infrared Raman laser under di-harmonic pumping was obtained with the H2 gas pressure of 3.4 MPa. The corresponding photon conversion efficiency was 41.9%, and peak power reached 9.4 MW.

An Integrated Millimeter-Wave Satellite Radiometer Working at Room-Temperature with High Photon Conversion Efficiency.

In this work, the design of an integrated radiometer frontend for earth observation applications on satellites is presented. By means of the efficient electro-optic modulation of a laser pump with the observed millimeter-wave signal followed by the detection of the generated optical sideband, a room-temperature low-noise receiver frontend alternative to conventional Low Noise Amplifiers (LNAs) or Schottky mixers is proposed. Efficient millimeter-wave to 1550 nm upconversion is realized via a nonlinear optical process in a triply resonant high-Q Lithium Niobate (LN) Whispering Gallery Mode (WGM) resonator. By engineering a micromachined millimeter-wave cavity that maximizes the overlap with the optical modes while guaranteeing phase matching, the system has a predicted normalized photon-conversion efficiency per pump power, surpassing the state-of-the-art by around three orders of magnitude at millimeter-wave frequencies. A piezo-driven millimeter-wave tuning mechanism is designed to compensate for the fabrication and assembly tolerances and reduces the complexity of the manufacturing process.

Converting Sewage Water into H2 Fuel Gas Using Cu/CuO Nanoporous Photocatalytic Electrodes.

This work reports on H2 fuel generation from sewage water using Cu/CuO nanoporous (NP) electrodes. This is a novel concept for converting contaminated water into H2 fuel. The preparation of Cu/CuO NP was achieved using a simple thermal combustion process of Cu metallic foil at 550 °C for 1 h. The Cu/CuO surface consists of island-like structures, with an inter-distance of 100 nm. Each island has a highly porous surface with a pore diameter of about 250 nm. X-ray diffraction (XRD) confirmed the formation of monoclinic Cu/CuO NP material with a crystallite size of 89 nm. The prepared Cu/CuO photoelectrode was applied for H2 generation from sewage water achieving an incident to photon conversion efficiency (IPCE) of 14.6%. Further, the effects of light intensity and wavelength on the photoelectrode performance were assessed. The current density (Jph) value increased from 2.17 to 4.7 mA·cm−2 upon raising the light power density from 50 to 100 mW·cm−2. Moreover, the enthalpy (ΔH*) and entropy (ΔS*) values of Cu/CuO electrode were determined as 9.519 KJ mol−1 and 180.4 JK−1·mol−1, respectively. The results obtained in the present study are very promising for solving the problem of energy in far regions by converting sewage water to H2 fuel.

ZnS/CZTS QDs modification for escalating photoelectrochemical properties of α-Fe2O3 thin film

Present study investigates the use of visible light active green CZTS quantum dots for boosting the photo-activity of hematite thin film towards efficient hydrogen generation. A photoelectrode has been prepared by depositing a passivating layer of ZnS on Cu2ZnSnS4 (CZTS) QDs sensitized hematite thin film (H-CZTS QDs/ZnS) for solar hydrogen production. These films were implemented as photoanode in photoelectrochemical cell for photoresponse measurements. XRD, HRTEM, FESEM and UV–vis diffuse reflectance spectroscopy (DRS) techniques were used to characterize these thin films for deeper analysis. The modified hematite film has showed 1.48 times more photocurrent density as compared to pristine counterpart. An increase in photocurrent could be attributed to better light absorption ability and reduced charge transfer resistance after modification. Applied bias to photon conversion efficiency was also calculated and found higher for modified sample.

Numerical modeling and performance optimization of carbon-based hole transport layer free perovskite solar cells

Owing to low production cost and ease of processing, hole-transport layer (HTL) free carbon electrode-based perovskite solar cells (c-PSCs) have emerged as a potential photovoltaic (PV) technology. Despite this, c-PCSs still have to achieve the high photon conversion efficiency exhibited by standard PSCs using HTLs. In the present work, device modeling of Csx(FA0.4MA0.6)1-xPbI2.8Br0.2 based HTL-free c-PSC was presented using the simulation program Solar Cell Capacitance Simulator (SCAPS). Output results were successfully replicated in the simulation that were comparable to experimentally reported values. Furthermore, several parameters affecting device performance, such as the absorber layer, the electron transport layer (ETL), front contact thicknesses, and doping concentrations, are studied and optimized. Additionally, the defect density at the perovskite/ETL interface is investigated. Under optimized conditions, a high open-circuit voltage of 1.13 V, short-circuit current density of 22.54 mA/cm2, fill factor of 79.75%, and photon conversion efficiency of 20.43% is achieved. Results demonstrate the promising features of the proposed HTL-free c-PSC. Lastly, the impact of temperature and work function of back metal contacts were also examined. The simulation results suggest a direction to design low-cost and highly efficient HTL-free c-PSCs.

Prediction of intermediate band in Ti/V doped γ-In2S3.

Materials with an intermediate energy band (IB) introduced in the forbidden gap are viable alternatives to tandem configurations of solar cells for increasing the photon-conversion efficiency. One of the aspiring designs proposed for the intermediate band concept is hyperdoped (Ti, V):In2S3. Being very important in copper indium gallium sulfide (CIGS) solar cells, indium thiospinel (In2S3) is known for its three different temperature as well as pressure, polymorphs. The most stable β-In2S3 was experimentally shown to have an isolated intermediate band (IB) and exhibits sub-band gap absorption due to the completely filled IB after V-doping. Though experimental observation holds a positive signature, recent DFT studies did not show a metallic intermediate band for the V dopant in the 3+ charge state. In order to clarify this, we have taken incentive from experimental XRD analysis that V-doped β-In2S3 shows peaks from disordered In vacancies (either α or γ), in addition to the ordered In vacancies expected. Hence, we have carried out state-of-the-art DFT based computations on pure and Ti, V-doped In2S3 in the γ-phase which has not been studied yet. We considered the Ti and V dopants in various charge states. Our theoretical study including hybrid functional, does in fact find the IB in V-doped γ-In2S3. However, at equilibrium the IB lies in between the Fermi level (EF) and conduction band minimum (CBM).

Enhanced Catalytic Activities of TiO₂ Nanotube Arrays Co-Sensitized with Pt/CdS/ZnS via Electrodeposition and Successive Ionic Layer Adsorption and Reaction (SILAR) Method Approach.

In this work, we have synthesized a nanocomposite ZnS/CdS/Pt/TiO₂ nanotube arrays (denoted ZCP-NTAs). Firstly, TiO₂ nanotube array (NTAs) material was fabricated by the anodic method of a titanium plate in an electrolyte solution containing 0.35 M NaHSO₄ and 0.24 M NaF and incubated in the air at 500 ºC for 2 hours. After that, pulsed electrodeposition technology was used to decorate platinum nanoparticles (denoted as Pt NPs) onto the surface of TiO₂ nanotubes to form P-NTAs photoelectrodes. Then, the SILAR method is used to deposition CdS quantum dots (symbolized as CdS QDs) on the surface of P-NTAs to form CP-NTAs material. Finally, by the SILAR method, a ZnS passive layer that protects against optical corrosion and inhibits recombination of e-/h+ pairs was coated onto the CP-NTAs to form ZCP-NTAs material. As-prepared ZCP-NTAs photocatalytic material has good absorbability of light in the visible region with light absorption wavelength up to 608 nm, photon conversion efficiency up to 5.32% under light intensity AM1.5G, and decomposition efficiency of 10 mg L-1 methyl orange (MO) in 120 minutes reached 91.50%. This material promises to bring high application ability in the photocatalytic field applied for environmental treatment and other applications.

Constructing two-dimensional heterojunction through decorating covalent organic framework with MoS2 for enhanced photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting is regarded as one of the most effective route to address energy crisis and environmental issues. Two-dimensional covalent organic frameworks (2D COFs) have made some advances in PEC water splitting owing to their functionalized building blocks, remarkable structural stability, and unique conjugated structures, etc. Unfortunately, the PEC performance of COFs is severely hindered because of the poor surface charge transfer, surface recombination at the photoanode/electrolyte junction, and sluggish oxygen evolution reaction (OER) kinetics. Herein, we report an efficient 2D heterojunction through decorating a 2D COF with MoS2 for enhanced PEC water oxidation. The photocurrent density and incident photon conversion efficiency (IPCE) of the resultant photoanode are effectively improved by constructing 2D COF-based heterojunction. Such a strategy of constructing 2D heterojunction can not only efficiently accelerate the charge separation and transfer but also promote the separation of photogenerated electron-hole pairs for oxygen evolution. This work provides rational suggestions for developing COF-based photocatalysts to address the energy crisis and various environmental issues.

Thickness Variation Effects on the Efficiency of Simulated Hybrid Cu2ZnSnS4-Based Solar Cells Using SCAPS-1D

This study presents the simulations of a hybrid Cu2ZnSnS4-based solar cell with a planar heterojunction structure in a hybrid model (n-FTO/n-ZnO/p-PSCS/p-CZTS/p-PSCS/p-HTM) using a One-Dimensional Solar cell capacitance simulator (SCAPS-1D). . The configuration "121" of the hybridizing absorber layers of the device was simulated and related with as-Copper Zinc Tin Sulphide (CZTS). The simulation used an absorber layer with a step-length thickness of 25 nm and thicknesses ranging from 100 nm to 500 nm. The bandgap diagram, I-V characteristics curve, percentage conversion efficiencies, and the quantum efficiencies of the simulated solar cells were calculated and constructed from simulated results. The percentage conversion efficiency of 22.57%, fill factor of 49.99%, open-circuit voltage of 0.80V, and short circuit current of 25.12 mAcm-2 were obtained. The obtained photon conversion efficiency shows that the hybridization of different absorber layers was achievable. It was also established that the performance efficiencies of hybrid CZTS structure in terms of optimum thickness and sandwiched Perovskite Solar cells model (FTO/ZnO/CZTS/PSCS/CZTS/HTM) has the same efficiencies for "121 configurations". On the other hand, the efficiencies of as- CZTS structures were higher than the PSCS configuration, which might be due to SCAPS-1D as it was originally designed for Thin Films Solar cells.

Ternary Ni0.5Zn0.5Fe2O4/carbon nanocomposite as counter electrode for natural dye-sensitized solar cells: Electro-photovoltaic characterizations

The most notable counter electrode (CE) in dye-sensitized solar cells is platinum (Pt), which is expensive and scarce. Here, Ni0.5Zn0.5Fe2O4/carbon (NZF/C) composites containing different ratios of carbon were synthesized and used as novel counter electrodes. NZF/Cs have specific surface areas of 109.3–128.6 m2 g−1, pore sizes of 99.4–119.6 Å, and bandgap energies of 2.36–2.99 eV, according to the characterization results. The catalytic activities of NZF/C CEs were verified by electrochemical impedance spectroscopy and cyclic voltammetry. NZF/Cs demonstrated outstanding catalytic activities in the reduction of I3− and had performance comparable to Pt CEs in the dye-sensitized AgNP/TiO2 DSSCs. For the natural betalain dye, NZF/C-1 CE demonstrated a 2.75% efficiency with a short circuit current density of 4.13 mA cm−2 and a fill factor of 50.71%, which was very competitive with Pt CE's 2.83% efficiency. During 30 days of stability testing, NZF/C-1 CE maintained a photon conversion efficiency of 7.18% and a fill factor of 55.57% for Z-907 synthetic dye. The high electrocatalytic activity of NZF coupled with the good conductivity of carbon black account for NZF/C performance. The results herein show that NZF/C can be used as a cost-effective and efficient substitute for Pt in DSSCs.